祝好(zhù hǎo) - best wishes (a letter or message sign-off) in Mandarin

祝好 (zhù hǎo) is a short sign-off used at the end of a letter, email, or message, roughly equivalent to "best wishes" or "kind regards" in English correspondence. 祝 (zhù) means "to wish (someone well)", the same character that opens 祝你好运 (zhù nǐ hǎo yùn, "good luck") and 祝你生日快乐 (zhù nǐ shēng rì kuài lè, "happy birthday").

It is a closing formula, not a spoken greeting: you would write 祝好 (zhù hǎo) at the bottom of a message but would not say it to someone's face on meeting them.

Note that AQA's own gloss for this entry ("best wishes/good luck") slightly overstates the "good luck" sense - 祝好 (zhù hǎo) on its own reads as a polite sign-off, not a wish of luck for a specific event. For "good luck" proper, 祝你好运 (zhù nǐ hǎo yùn) or 加油 (jiā yóu, "keep it up") are the natural choices.